Compound semiconductor materials, eg materials such as gallium arsenide, indium phosphide, gallium phosphide and cadmium mercury telluride, are well known materials having uses in the electronics industry in such applications as microwave oscillators, semiconductor light emitting diodes and lasers, and infrared detectors.
Such materials have been made in the past by forming, usually on a substrate crystal, one or more active layers, by the method of vapour phase epitaxy (VPE).
It has been known for some time to produce by VPE compound semiconductors of the form M.sup.A Q.sup.A where M.sup.A is Group III element and Q.sup.A is Group V element by reacting a trialkyl of the element M.sup.A with a gaseous compound, eg a hydride, of the Group V element Q.sup.A. This method is a suitable method of preparing gallium arsenide from Ga(CH.sub.3).sub.3 and AsH.sub.3 for example.
Consequently, trialkyl gallium compounds, in particular trimethyl gallium, have become important in the production of semiconductor materials.
It is well known to those skilled in the art that the presence of impurities in semiconductor materials has a profound effect on the electrical and other properties of the materials. In order to control the properties it is therefore desirable to produce such materials in a high purity form. This means that the precursor materials such as trialkyl gallium compounds used in the manufacture of the semiconductor materials are desirably as pure as possible.
The reaction between gallium trichloride and a Grignard reagent containing an alkyl radical is known but has not hitherto been used for the preparation of trialkyl gallium compounds. This is because the reaction has been carried out is diethyl ether as solvent and has resulted in the formation of trialkyl gallium-diethyl ether adducts. Such adducts cannot be broken down directly into the trialkyl gallium compound without severe contamination from the ether.